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<br />precipitation-frequency values (Reference 43). The discharges were calculated for <br />fully developed basin conditions. <br /> <br />Peak discharges for the South Platte River were determined as part of the <br />September 1985 UDFCD Flood Hazard Area Delineation report (Reference 44). <br />Peak-frequency values for the South Platte River were taken from the May 1983 <br />Hydrologic Study report prepared by Merrick and Company under contract to the <br />UDFCD (Reference 45). <br /> <br />Peak discharge-drainage area relationships for all streams studied by detailed s__- <br />methods are shown in Table 2. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of flooding from the sources studied were <br />carried out to provide estimates of the elevations of floods of the selected recurrence <br />intervals. <br /> <br />Locations of selected cross sections used in the hydraulic analyses are shown on the <br />Flood Profiles (Exhibit 1). For stream segments where a floodway was computed <br />(Section 4.2), selected cross section locations are also shown on the FIRM. <br /> <br />3.3 Vertical Datum <br /> <br />All FIS reports and FIRMs are referenced to a specific vertical datum. The vertical <br />datum provides a starting point against which flood, ground, and structure elevations <br />can be referenced and compared. Until recently, the standard vertical datum used for <br />newly created or revised FIS reports and FIRMs was the National Geodetic Vertical <br />Datum of 1929 (NGVD). With the completion of the NA VD, many FIS reports and <br />FIRMs are now prepared using NA VD as the referenced vertical datum. <br /> <br />Flood elevations shown in this FIS report and on the FIRM are referenced to the <br />NA VD. These flood elevations must be compared to structure and ground elevations <br />referenced to the same vertical datum. For information regarding conversion <br />between the NGVD and NA VD, visit the National Geodetic Survey website at <br />www.ngs.noaa.gov, or contact the National Geodetic Survey at the following <br />address: <br /> <br />Vertical Network Branch, N/CG13 <br />National Geodetic Survey, NOAA <br />Silver Spring Metro Center 3 <br />1315 East-West Highway <br />Silver Spring, Maryland 20910 <br />(301) 713-3191 <br /> <br />Temporary vertical monuments are often established during the preparation of a flood <br />hazard analysis for the purpose of establishing local vertical control. Although these <br />monuments are not shown on the FIRM, they may be found in the Technical Support <br />Data Notebook associated with the FIS report and FIRM for this community. <br />Interested individuals may contact FEMA to access these data. <br /> <br />17 <br />